I'm extremely frustrated with this class that I have now and the time they are taking on tests!!!! SO I'm going to ask you all...
Is 30 minutes enough time to take a Science test with 6 vocab questions 4 multiple choice and 4 short answer/essay questions?

Personally, I think 30 minutes is not enough time. I can see my 4th graders taking 30 minutes just on the short answer/essay questions. Are you looking for a sentence? Paragraph?

I always give at least 45 minutes on a test (except spelling) because kids work at varying degrees when working independently. I also make sure each student has a silent reading book-something to do that is not distracting other students who are not finished.

I know that many of my grade 5 and 6 students would struggle with completing the test in that amount of time, particularly if they need to write more than one or two sentences for the short answer and essay questions. Even with review, my students need time to process the questions and formulate their responses, ensuring that they are well-organized and contain all of the required information. I always consider how many students were able to complete the test in the time I have given them. If many weren't able to finish it, then I allow them more time.

__________________It does not matter how slowly you go so long as you do not stop
Confucius

Are the vocab questions matching, write definitions, fill in the blank, etc?

How many choices are you providing for the multiple choice and are the answers a phrase, sentence, word?

Fill in the blank vocab and 4 choices for multiple choice.

I don't really "call" them essays. I actually don't really label the sections just give directions and my directions on the essay/short answer portion is "answer the following questions in complete sentences." I go over my expectations for what these answers should look like the day before each test.

ANYWAY, I suppose 30 minutes is not enough time. I will have to move my schedule around on test days I guess and figure out a better way to do this!
I'm most frustrated, however, because if I give them a longer period of time then I have students that won't even finish their test in an HOUR! but then I get their papers back and there are drawings all over them and watching them shows me their not really using their time wisely.

While I also have my student or two that takes a long time on tests, I have more that go too quickly on tests. It depends on the type of test. On the tests that are quick recall that only require rote learning, I don't give them a lot of time. If I really want them to think and write quality answers, I tend to give them lots and lots of time. Your test seems to be a bit in between.

I am not saying you should do this suggestion, but here is one IF you really want students to speed up during a test. Limit their choices when they are finished with the test, but let them know that 30 minutes after the test has begun you will let them know it has been 30 minutes. You will then collect tests of those who are finished. Then allow 3-6 really fun quiet choices that students can do who are finished (use the computer for educational games, quiet centers etc. The others who aren't finished may finish. Those who make any noise in the fun activities will only be allowed to do a worksheet that you have.)

The only problem, that you probably have realized, is that some students might hurry too quickly after the 30 minutes. Good luck to you. :-)